The present invention, generally, relates to the field of simulation and, more particularly, to a computer-generated image system with limited data processing capacity for real-time operation.
In previous scanline type of computer-generated image systems, there was a limitation on the total number of polygon edge crossings per scanline. It was necessary to arrange databases such as to avoid exceeding this limit. Since this parameter can change rapidly line to line and from frame to frame, it has not been possible to use measurements taken at the output in order to control image content, such as to prevent overload in real-time operation.
In the event that overload occurred, the video from the last previous non-overload scanline was repeated for the current scanline. The result was a vertical stretching of the image in the area of the overload. This anomaly was less objectionable than the streaks which would appear if the overload line were displayed.
In the simulator field which today uses increasingly the computer-generated image system, a somewhat similar type of overload can occur if the pixel processors do not have time to complete the processing of a field before the field is due to be displayed. It might be possible to redisplay the last non-overload field until the overload problem could be corrected, but this would result in distracting discontinuity of motion.
Alternatively, it may be possible to delay the start of display of a new field until the processing is completed. This would be difficult to accommodate in the display system and would likely result in intensity fluctuation or "flicker".
The fact that an overload occurs on a field rather than on an individual scanline means that changes in loading are based on the average over the field and occur more gradually than in a scanline type system which overloads due to peak conditions occurring on a single scanline. This fact permits data taken on one field to be used to correct the loading on subsequent fields.
This load correction can be accomplished by changing the switching distances which control the level of detail with which scene elements are portrayed. However, the strategy for changing smoothly various levels of detail calls for the use of transparency, which causes increased load on a video processor.
Also, some instances of use call for very rapid field to field changes in scene content. In this case, the data taken from a previous field cannot be used to adjust the scene content of the following field, because this technique would result in abrupt and distracting changes in scene content.
Accordingly, it is a principal object of the present invention to provide in a computer-generated image system a way of avoiding any overload to cause such image degradation.
It is also an object of the present invention to provide a means of preventing overload in the video processor portion of a computer-generated image system, particularly as used in the simulation field.